The present invention relates to methods for producing high quality laser-induced damage images (in particularly 3D portraits) in transparent objects using high power laser radiation on basis of the breakdown phenomenon.
A number of techniques for creating a variety of patterns on the surface and inside of transparent substrates using pulsed laser radiation are well known.
One publication disclosing such techniques is the Russian invention #321422 to Agadjanov et. al., published on Nov. 16, 1970 (#140454529-33). The invention concerns a method of manufacturing decorative products inside a transparent material by changing the material structure by laser radiation. As disclosed, by moving a material relative to a focused laser beam, it is possible to create a drawing inside the material.
U.S. Pat. No. 3,715,734 to Fajans discloses a three-dimensional memory storage unit, which is prepared by carbonizing selected spots in a block of polymethylmethacrylate by means of a steeply converging laser beam. The energy of the beam is applied in pulses of such duration and at such intensity that carbonization takes place only at the focal point of the beam.
U.S. Pat. No. 4,092,518 to Merard discloses a method for decorating transparent plastic articles. This technique is carried out by directing a pulsed laser beam into the body of an article by successively focusing the laser beam in different regions within the body of the article. The pulse energy and duration is selected based upon the desired extent of the resulting decorative pattern. The effect of the laser is a number of xe2x80x9cmacro-destructionsxe2x80x9d (fissures in the material of the article) appearing as fanned-out cracks. The pattern of the cracks produced in the article is controlled by changing the depth of the laser beam focus along the length of the article. Preferably, the article is in the form of a cylinder, and the cracks are shaped predominantly as saucer-like formations of different size arranged randomly around the focal point of the optical system guiding a laser beam. The device used to carry out this technique is preferably a multi-mode solid-state, free-running pulse laser used in conjunction with a convergent lens having a focal length from 100 to 200 mm.
U.S. Pat. No. 4,843,207 to Urbanek et al. discloses a method of creating controlled decorations on the surface of a hollow symmetrical transparent article. This technique is preferably carried out on glass. The glass is preconditioned with a coating on the outer surface of the glass being approximately 1.2 mm thick and made of a material having at least 75% absorption of laser radiation. The technique is also carried out using a laser having a wave of length of 0.5 to 2 microns acting upon the external coating through the wall of the cylindrical glass article. The laser beam moves so that it is focused on the surface of the cylinder, and moves about the axis of symmetry of the cylinder to irradiate the aforementioned surface coating. As a result, the irradiated portions of the surface coating go through a phase change and a pattern is formed.
U.S. Pat. No. 5,206,496 to Clement et al. discloses a method and apparatus for providing in a transparent material, such as glass or plastic, a mark which is visible to the naked eye or which may be xe2x80x9cseenxe2x80x9d by optical instruments operating at an appropriate wavelength. The Clement et al. Patent describes a method and apparatus for producing a subsurface marking which is produced in a body such as bottle, by directing into the body a high energy density beam and bringing the beam to focus at a location spaced from the surface, so as to cause localized ionization of the material. In the preferred embodiment the apparatus includes a laser as the high energy density beam source. The laser may be a Nd-YAG laser that emits a pulsed beam of laser radiation with a wavelength of 1064 nm. The pulsed beam is incident upon a first mirror that directs the beam through a beam expander and a beam combiner to a second mirror. A second source of laser radiation in the form of a low power He-Ne laser emits a secondary beam of visible laser radiation with a wavelength of 638 m. The secondary beam impinges upon the beam combiner where it is reflected toward the second reflecting surface coincident with the pulsed beam of laser radiation from the Nd-YAG laser. The combined coincident beams are reflected at the reflecting surface via reflecting two other surfaces to a pair of movable mirrors for controlling movement of the beam. The beam then passes through a lens assembly into the body to be marked.
Soviet patent publication 1838163 to P. V. Agrynsky, et. al discloses a process for forming an image in a solid media by processing of the optically transparent solid material by a beam of radiation with changeable energy for creation of the image.
WIPO Patent Document No. 96/30219 to Lebedev et al. discloses a technology for creating two- or three-dimensional images inside a polymer material using penetrating electromagnetic radiation. The technology can be used for marking and for producing decorative articles and souvenirs. Specifically, laser radiation is used as the penetrating radiation, and carbonizing polymers are used as the polymer material. By these means, it is possible to produce both black and half-tone images in the articles.
U.S. Pat. No. 5,575,936 to Goldfarb discloses a process and apparatus where a focused laser beam causes local destruction within a solid article, without effecting the surface thereof. The apparatus for etching an image within a solid article includes a laser focused to a focal point within the article. The position of the article with respect to the focal point is varied. Control means, coupled to the laser, and positioning means are provided for firing the laser so that a local disruption occurs within the article to form the image within the article.
U.S. Pat. No. 5,637,244 to Erokhin discloses a technique which depends on a particular optical system including a diffraction limited Q-switched laser (preferably a solid-state single-mode TEM00) aimed into a defocusing lens having a variable focal length to control the light impinging on a subsequent focusing lens that refocuses the laser beam onto the transparent article being etched. The laser power level, operation of the defocusing lens, and the movement of the transparent article being etched are all controlled by a computer. The computer operates to reproduce a pre-programmed three-dimensional image inside the transparent article being etched. In the computer memory, the image is presented as arrays of picture elements on various parallel planes. The optical system is controlled to reproduce the stored arrays of picture elements inside the transparent material. A method for forming a predetermined half-tone image is disclosed. Accordance to the method, microdestructions of a first size are created to form a first portion of the image and microdestruction of a second size different from the first size are created to form a second portion of the image. Microdestructions of different sizes are created by changing the laser beam focusing sharpness and the radiation power thereof before each shot.
U.S. Pat. 5,886,318 to A. Vasiliev and B. Goldfarb discloses a method for laser-assisted image formation in transparent specimens, which consists in establishing a laser beam having different angular divergence values in two mutually square planes. An angle between the plane with a maximum laser beam angular divergence and the surface of the image portion being formed is changed to suit the required contrast of an image. EPO Patent Document 0743128 to Balickas et al. disclose a method of marking products made of transparent materials which involves concentration of a laser beam in the material which does not absorb the beam, at a predetermined location, destruction of the material by laser pulses and formation of the marking symbol by displacement of the laser beam. Destruction of the material at that location takes place in two stages. In the first stage, the resistance of the material to laser radiation is altered, while, in the second stage, destruction of the material takes place at that location.
Russian patent publication RU 20082288 to S. V. Oshemkov discloses a process for laser forming of images in solid media by the way of focusing of laser radiation in a point inside a sample which differs by following: with the aim to save the surface and the volume of the sample before the definite point and creation of three dimensional images, the sample is illuminated with the power density higher than the threshold of volume breakdown and moving the sample relatively to the laser beam in three orthogonal directions.
U.S. Pat. No. 6,087,617 to Troitski et al. discloses a computer graphic system for producing an image inside optically transparent material. An image reproducible inside optically transparent material by the system is defined by potential etch points, in which the breakdowns required to create the image in the selected optically transparent material are possible. The potential etch points are generated based on the characteristics of the selected optically transparent material. If the number of the potential etch points exceeds a predetermined number, the system carries out an optimization routine that allows the number of the generated etch points to be reduced based on their size. To prevent the distortion of the reproduced image due to the refraction of the optically transparent material, the coordinates of the generated etch points are adjusted to correct their positions along a selected laser beam direction.
U.S. patent application Ser. No. 09/354,236 to Troitski discloses a laser-computer graphic system for generating portrait and 3-D reproductions inside optically transparent material. The invention discloses the method for production of a portrait with the same gray shades like a computer image by using a multi-layer picture. Points of every layer are arranged so that the distance between adjacent etch points are equal to the minimal distance between etch points that can be provided without the breakage of the material. Every layer is parallel with respect to the portrait plane, and distance between parallel planes is set equal to minimal distance at which the breakage of the material does not occur.
U.S. patent application Ser. No. 09/557,306 to Troitski discloses method and laser system for creation of laser-induced damages to produce high quality images. Accordance to the invention, a laser-induced damage is produced by simultaneously generating breakdowns in several separate focused small points inside the transparent material area corresponding to this etch point. Damage brightness is controlled by variation of a number of separate focused small points inside the transparent material area.
U.S. patent application Ser. No. 09/583,454 to Troitski discloses method and laser system controlling breakdown process development and space structure of laser radiation for production of high quality laser-induced damage images. Accordance to the invention, at the beginning an applied laser radiation level just exceeds an energy threshold for creating a plasma condition in the material, and thereafter the energy level of the applied laser radiation is just maintain the plasma condition. Accordance to another method a laser generates a TEMmn radiation. The values of the integers m and n are controlled and determined so as to reproduce particular gray shades for a particular point of an image.
Laser-induced damage image is a plurality of damages inside a transparent material created by a pulsed laser beam, which is periodically focused at predetermined points of the material. These damages become visible by scattering the exterior light. It is clear, that visual appeal of a damage image is defined by two facts: the firstxe2x80x94scattering signature of the damages and the secondxe2x80x94the way by which the damages are arranged to reproduce the image.
Analyzing the methods of all aforementioned Patents it is clear that almost of them disclose creation of laser-induced damages and teach to displace mutually a transparent material and a laser beam in order to establish a next damage. However the Patents do not disclose how the damages should be replaced inside a transparent material to reproduce the right image with high quality. Only two Patents and one Patent Application touch on the problem: U.S. Pat. No. 5,637,244 to Erokhin; U.S. Pat. No. 6,087,617 to Troitski et al. and U.S. patent application Ser. No. 09/354,236 to Troitski.
In particularly, U.S. Pat. No. 5,637,244 to Erokhin disclose a method for forming a predetermined decorative image inside a transparent material xe2x80x9cwherein the focusing step comprises moving the transparent material relative to the laser beam perpendicularly to the laser beam to create microdestructions that form a first two-dimensional plane section of the decorative image, said first plane section appearing as a first array of image elements of the decorative imagexe2x80x9d. Thereby the patent teaches how the damages should be produced in order that previous damage does not hinder next damage but the patent does not disclose how to create such damage arrangement or in other words, how the damages should be replaced in space of a material to produce high quality images.
U.S. Pat. No. 6,087,617 to Troitski et al. and U.S. patent application Ser. No. 09/354,236 to Troitski disclose methods of damage arrangements, however, the methods do not give a chance to produce 3D portraits of high quality. Indeed, the base of these methods is the production of laser-induced damage images containing damages with minimal distance between them more than d0 (if the distance between adjacent damages is smaller than d0, the internal split can occur). Consequently, such images have two principal particularities, which for 3D portraits became general defects: the firstxe2x80x94since minimal distance between adjacent damages is not equal to zero, total number of damages in an image is smaller than total number of pixels in the computer image and therefore the spatial resolution of the image produced inside transparent material is smaller than the applicable computer image; the secondxe2x80x94since the distance between adjacent damages is not equal to zero and usually it is about the damage size, you will see the clearance surface of such 3D image although you will look at its face. The last factor decreases portrait contrast, creates noise background, match front and back images. All this decreases 3D portrait quality essentially. Consequently, such 3D portraits have bad quality and, for practical purposes, only halfxe2x80x943D portraits (without the back sections) are produced.
The invention discloses the method for production of 3D portraits without these defects.
The present invention has its principal task to provide a method for production of high quality laser-induced damage 3D portraits, which has the same space resolution as the applicable computer model and which has sufficiently tight front face, right and left profiles so that the clearance surface does not interfere the front surface and the right (left) profile does not interfere the left (right) profile.
One or more embodiments of the invention comprise a method for reformation of 2D portrait into the multi-layers image, consisting of several parallel planes covering such arrangement of pixels that the said multi-layers image has the same number of pixels as the corresponding 2D portrait and the said multi-layers image can be produced inside the transparent material without internal split.
One or more embodiments of the invention comprise a method for reformation of the 3D computer portrait into several 3D computer models having the same orientation and covered by pixels so that total number of their pixels is equal to the total number of unmodified 3D portrait pixels and all damages corresponding to the pixels can be produced inside the transparent material without internal split.
One or more embodiments of the invention comprise a method arranging the pixels so that the time production of the damages corresponding the pixels is minimal and for using focusing optical system any damage, which has been produced is not the barrier for production of following damages.